Introduction

Many commonly held beliefs and practices in jaw and oral-facial pain problems are not supported by scientific evidence. There is also a discrepancy between clinical dental practice and scientific advances in neurobiology and the understanding of pain. The public believes that jaw pain problems (temporomandibular disorders, or TMD) are a dental condition requiring dental treatments. Physicians routinely refer and defer to dentists, further supporting the widespread belief that TMD is a dental disorder. This has led to an explosion of irreversible, sometimes harmful, invasive treatments for TMD unsupported by evidence of efficacy—while accumulating evidence has revealed no convincing need or indication for dental treatments in most TMD.

TMD, a muscle pain disorder

TMD is a nonspecific term representing a variety of painful and/or dysfunctional conditions involving the masticatory muscles and the temporomandibular joint (TMJ).[1] The most common TMD (90% to 95% of cases) is nonstructural masticatory muscle pain, sometimes presenting in individuals involved in a motor vehicle collision (MVC).[2] The Quebec Task Force on Whiplash-Associated Disorders (WAD) noted TMD may be manifested with any severity-grade of whiplash.[3]

Legal jawlash!

The term jawlash was popularized in the media in the 1970s to represent a wide variety of jaw pains, sounds, dysfunctions, and symptoms, many of which were unrelated to the jaw, and that were allegedly related to violent, uncontrolled forces that snapped patients’ heads around and supposedly misaligned the jaws. TMD purportedly caused by a whiplash-type mechanism (acute hyperextension-flexion of the neck) to the TMJ has been shown to be an unlikely event, linked anecdotally and disproved experimentally.[4-6] Physical injury to jaw structures is an improbable mechanism for most TMD complaints following whiplash-type injuries. MVC-TMD causation controversies are primarily legal, and legal causation does not correlate with medical causation. The medical etiology of most TMD is incompletely understood; presently considered a multifactorial biopsychosocial disorder.[1] Legal causation relates to the requirement to establish a probable cause—a relationship between the patient’s TMD and the motor vehicle collision at a standard of more likely than not, which would be unacceptable by medical standards. TMD may be legally caused by a motor vehicle collision, but has not been proven to be medically caused by a motor vehicle collision.[7]

TMJ structure

The jaw signs and symptoms of most TMD are understood to represent a complex interaction between a spectrum of normal and adaptive TMJ conditions, neurophysiology, and psychological issues. The majority of TMJ sounds are not associated with pain and are present in large portions of the non-TMD-patient population.[8] The TMJ is a non-weight bearing low-contact pressure joint whereby the contact surfaces are fibrocartilage (growth cartilage) rather than epiphyseal cartilage, which makes it quick healing and highly adaptable. Many apparent TMJ image abnormalities are present in asymptomatic patients, and probably represent the adaptive changes in a unique joint, not injury or pathological degenerative joint disease.[9] The rapidly changing understanding of pain involves a number of mechanisms in peripheral and central tissues that regulate the excitability of nociceptive afferents at several levels involving the transmission, integration, and regulation of nociceptive signals. These mechanisms interact with perceptual, autonomic, neuroendocrine, and emotional systems resulting in a highly personal pain experience. The relationship between persistent pain and motor signs and symptoms, the Pain-Adaption Model,[10] is clinically termed myofascial pain and dysfunction. It is the commonest manifestation of TMD, and hypothesizes that activation of nociceptors in jaw muscles and adjoining structures can inhibit agonist motor neurons through segmental reflexes and modification of motor neuron patterns similar to nociceptors in skin, muscle, connective tissue, and joints. Peripheral stimulation of sensitized pain pathways is felt to be associated with chewing and parafunctional jaw muscle activity (bruxing and clenching habits). The transition from acute to chronic pain remains an area of investigation that will lead to advances in the understanding, prevention, and treatment of chronic nonstructural pain and TMD. 

TMD-associated symptoms

The characteristics of patients with TMD that appear to be related to motor vehicle collisions differ from TMD unrelated to motor vehicle collisions in terms of the psychosocial components, not in physical factors. TMD patients alleging motor vehicle collision causation show greater levels of facial and headache pain, jaw muscle and neck tenderness, and greater sleep disturbance than non-MVC-TMD. TMD patients litigating motor vehicle collision issues present with higher levels of pain, more masticatory muscle tender sites, greater utilization of health care and medications, higher levels of somatization, and higher pain assessments than non-litigating TMD patients. This suggests that litigation is an important factor in these patients.[11-13] It is prudent to understand the importance of psychological factors in MVC-TMD cases considering the evidence of nonstructural whiplash-related pain being unrelated to the initial injury and independent of the trauma.[14,15] 

TMD management

The present standard of therapy for common nonstructural TMD is conservative, noninvasive, reversible pain management with multidisciplinary cognitive and behavioral therapy, masticatory muscle relaxation, and jaw habit (clenching/bruxing) modification measures.[1] Dental orthotics (splint, bite plate, and so on) have no scientific evidence of efficacy beyond placebo effect, and are commonly used because patients want or perceive a benefit.[16] At the least, such devices should not cause changes in tooth or jaw positioning. After establishing a diagnosis, physicians can provide accurate information emphasizing patient understanding of a nonstructural, non-dental pain disorder. Counseling to alter patterns of negative thoughts and dysfunctional attitudes and foster healthy adaptive thoughts, emotions, and actions is indicated.[17] Appropriate patient self-management includes warm compresses, soft diet, and cessation of gum-chewing. There is no basis for the use of any painful therapies; jaw manipulation and chiropractic jaw treatments may prolong, propagate, and complicate the disorder.[18] Irreversible treatments like orthodontics, bite adjustments, tooth restorations, and surgery are usually inappropriate for TMD.[18]

Summary

Health care professionals now recognize advances in the understanding of pain and pain management for multifactorial biopsychosocial disorders like TMD. Physicians must better recognize the early signs and symptoms of TMD and understand the importance of early diagnosis and appropriate management, as well as the relationships between TMD and more widespread musculoskeletal pain disorders like fibromyalgia.[19,20]

Hope for the future

The future will see physicians recognizing the dental literature,[21] and dentists will continue to participate and lead in research, education, and management of oral facial pain as one of several disciplines acting in a coordinated manner to benefit chronic pain patients. However, in the case of TMD, we will use pain-management skills instead of dental procedures. Advances in our knowledge of pain will further elucidate the many factors interacting in TMD and chronic pain patients, and allow early identification of individuals at risk for chronicity as well as the biological and psychosocial risk factors associated with TMD. The role of litigation and secondary gain will become better understood, leading to a time when medical and legal concepts of chronic pain causation are more evidence-based and logically related.

Competing interests

None declared.

Burton H. Goldstein, DMD, MS, FRCDC

Dr Goldstein is in private practice as a specialist in oral medicine and oral and maxillofacial surgery. He is clinical associate professor at the University of British Columbia Faculty of Dentistry.